1. Field of the Invention
The present invention relates to an organic light emitting device and a method of driving the same.
2. Discussion of the Background
A pixel of an organic light emitting device includes an organic light emitting element and a thin film transistor (TFT) that drives the same.
The TFT may be classified into a polysilicon TFT and an amorphous silicon TFT according to the kind of an active layer included in the TFT. An organic light emitting device using a polysilicon TFT may have high electron mobility, good high frequency operation characteristics, and a low leakage current. However, it may not be easy to uniformly form characteristics of a semiconductor included in a TFT in a process of manufacturing an active layer with polysilicon. That is, a threshold voltage or mobility of the TFT may be different in each transistor. Accordingly, a luminance deviation may occur between a plurality of pixels that are included in the display device. Also, as a current is continuously supplied to an organic light emitting element, a threshold voltage of a polysilicon TFT may change and thus characteristics thereof may be degraded. Accordingly, even if the same data voltage is applied, a non-uniform current may flow to an organic light emitting element, and thus picture quality of the organic light emitting device may be degraded.
When a current flows for a long time period, the organic light emitting element may be degraded. Accordingly, even if the driving transistor applies a uniform current to the organic light emitting element, due to degradation of the organic light emitting element, luminance may decrease and thus picture quality may be deteriorated due to an afterimage, etc.
A hold type of flat panel display device such as an organic light emitting device displays a fixed image for a predetermined time period, for example for one frame, regardless of whether a still picture or a motion picture is displayed. For example, when displaying some object that continuously moves, the object stays at a specific position for one frame and stays at a position to which the object moves in a next frame, and thus motion of the object is discretely displayed. An object in a hold type display device moves after a time period of one frame. Because a time period of one frame is a time period in which an afterimage is sustained, even if the motion of the object is displayed in the way described above, the motion of the object may be continuously viewed.
However, when viewing a continuously moving object through a screen, because a line of sight of a person continuously moves along a motion of the object, the line of sight of a person collides with a discrete display method of the display device and thus a blurring phenomenon of a screen may occur. For example, it is assumed that the display device displays as an object stays at a position A in a first frame and at a position B in a second frame. In the first frame, a line of sight of a person moves from the position A to the position B along an estimated movement path of the object. However, the object may not be actually displayed at an intermediate position, and may only be displayed at the positions A and B.
Finally, because luminance recognized by a person for the first frame may be an integrated value of luminance of pixels in a path between the position A and the position B, i.e. an average value between luminance of an object and luminance of a background, an object may be blurredly viewed.
Because a degree in which an object is blurredly viewed in a hold type display device may be proportional to a time period in which the display device sustains the display, a so-called impulse driving method in which an image is displayed for only a partial time period within one frame and a black color is displayed for the remaining time period has been suggested.